As a demand for a high-speed wireless service is gradually increased, an improvement on a practical transfer rate per band is required to handle more subscribers according to an increment of a data transfer rate while guaranteeing a Quality of Service (QoS).
Recently, an Orthogonal Frequency Division Multiplex Access (OFDMA) wireless network which is based on Orthogonal Frequency Division Multiplex (OFDM) attracts public attention. As an advantage of an OFDMA modem, electric power and speed are optimally allocated between narrow-band subcarriers, and a guide band is not needed when a channel is divided within OFDMA, whereby frequency use efficiency is improved.
There is a technique for preventing interference by dividing a communication band into three sub channels when dividing into three sectors using one frequency utilizing the above features. That is, there is a technique for dividing one frequency into three segments.
FIG. 1 illustrates a configuration of an OFDMA frame which is not divided into segments according to IEEE 802.16e. FIG. 2 illustrates a configuration of an OFDMA frame which is divided into three segments.
In a configuration of a frame, when not dividing into segments, user data can be allocated to all sub channels, but when segmenting, the number of sub channels allocated to each segment is reduced to a third (⅓).
Segmentation is necessary in an area in which interference occurs between radio signals from a plurality of sectors, that is, “sector interference area”. However, segmentation is not necessary in the other places since there occurs no or little interference. Therefore, if segmentation is performed at each time, communication band use efficiency deteriorates.
As a technical document related to OFDMA, “MULTI-CARRIER COMMUNICATION WITH TIME DIVISION MULTIPLEXING AND CARRIER-SELECTIVE LOADING” is disclosed in Patent Document 1.
Patent Document 1: Japanese Patent Application National Publication (Laid-Open) No. 2004-529527